Listener and Source Moving

Q. A boy is walking away from a wall at a speed of 1.0 m/s in a direction at right angles to the wall. The boy blows a whistle steadily. An observer towards whom the boy is moving hears 4 beats/s. If the speed of sound is 340 m/s, the frequency of whistle is

1. 480 Hz
2. 680 Hz
3. 840 Hz
4. 1000 Hz

Q.

A source of sound emitting a note of frequency 200 Hz moves towards an observer with a velocity $v$ equal to the velocity of sound. If the observer also moves away from the source with the same velocity $v$, the apparent frequency heard by the observer is

1. 50 Hz
2. 100 Hz
3. 150 Hz
4. 200 Hz

Q.

A siren placed at a railway platform is emitting sound of frequency 5 kHz. A passenger sitting in a moving train A, records a frequency of 5.5 kHz while the train approaches the siren. During his return journey in a different train B, he records a frequency of 6.0 kHz while approaching the same siren. The ratio of the velocity of train B to that of train A is

1. $\frac{242}{252}$

2. 2

3. $\frac{5}{6}$

4. $\frac{11}{6}$

Q. An engine running at speed v/10 sounds a whistle of frequency 600 Hz. A passenger in a train coming from the opposite side at speed v/15 experiences this whistle to be of frequency f. If v is speed of sound in air and there is no wind, f is nearest to

1. 711 Hz
2. 630 Hz
3. 580 Hz
4. 510 Hz